Field of the Disclosure
Embodiments of the present disclosure generally relate to radar systems, and more specifically relate to measurement of phase noise in a cascaded radar system.
Description of the Related Art
A new class of safety systems, referred to as advanced driver assistance systems (ADAS), has been introduced into automobiles to reduce human operation error. These systems are enabled by smart sensors based primarily on millimeter-wave automotive radars. The proliferation of such assistance systems, which may provide functionality such as rear-view facing cameras, electronic stability control, and vision-based pedestrian detection systems, has been enabled in part by improvements in microcontroller and sensor technologies. Enhanced embedded radar-based solutions are enabling complementary safety features for ADAS designers.
In an automotive radar system, one or more radar sensors may be used to detect obstacles around the vehicle and the speeds of the detected objects relative to the vehicle. A processing unit in the radar system may determine the appropriate action needed, e.g., to avoid a collision or to reduce collateral damage, based on signals generated by the radar sensors. Current automotive radar systems are capable of detecting objects and obstacles around a vehicle, the position of any detected objects and obstacles relative to the vehicle, and the speed of any detected objects and obstacles relative to the vehicle. Via the processing unit, the radar system may, for example, alert the vehicle driver about potential danger, prevent a collision by controlling the vehicle in a dangerous situation, take over partial control of the vehicle, or assist the driver with parking the vehicle.
Automotive radar systems are required to meet the functional safety specifications of International Standard 26262 titled “Road Vehicles—Functional Safety.” ISO 26262 defines functional safety as the absence of unreasonable risk caused by malfunctioning behavior of electrical/electronic systems. Functional safety in automotive radar is the prevention of harm to humans due to failure of components in the radar. For automotive radar, the radar should be known to be functioning appropriately within a fault tolerant time interval of approximately 100 milliseconds (ms). Thus, while the vehicle is operating, a failure in any part of the radar that would lead to a degraded signal-to-noise ratio (SNR) should be detected, and an appropriate response performed within approximately 100 ms.
Phase noise has an important degradation effect in automotive radar systems such as Frequency Modulated Continuous Wave (FMCW) radar systems as an unacceptable level of phase noise may mask out objects with weaker signals since objects are detected at frequency offsets of the carrier. Automotive radar systems are typically designed to minimize phase noise but when in use in a vehicle, the phase noise may degrade (increase) due to a failure in the system, e.g., a transistor or piece of metal breaks. Therefore, to meet functional safety standards, it is important to monitor phase noise during vehicle operation and generate an appropriate response when the phase noise degrades to an unacceptable level. A typical requirement is to alert the vehicle driver if phase noise increases by approximately 12 decibels (dB).